Many accidents are caused by late braking and/or braking with insufficient force. A driver may brake too late for several reasons: he/she is distracted or inattentive; visibility is poor, for instance when driving towards a low sun; or a situation may be very difficult to predict because the driver ahead is braking unexpectedly. Most people are not used to dealing with such critical situations and do not apply enough braking force to avoid a crash.
Intelligent Emergency Braking (IEB) systems improve safety in two ways: firstly, they help to avoid accidents by identifying critical situations early and warning the driver; and secondly they reduce the severity of crashes which cannot be avoided by lowering the speed of collision and, in some cases, by preparing the vehicle and restraint systems for impact.
Most IEB systems use radar or lidar-based technology to identify potential obstacles ahead of the car. This information is combined with what the car knows of its own travel speed and trajectory to determine whether or not a critical situation is developing. If a potential collision is detected, IEB systems generally (though not exclusively) first try to avoid the impact by warning the driver that action is needed. If no action is taken and a collision is still expected, the system will then apply the brakes. Some systems apply full braking force, others an elevated level. Either way, the intention is to reduce the speed with which the collision takes place. Some systems deactivate as soon as they detect avoidance action being taken by the driver.
A known system is designed to help avoid or to mitigate accidents involving collisions with the rear of preceding traffic, either moving or stationary. Two long range radars, positioned at the front of the car, detect vehicles ahead which the car is likely to hit unless action is taken. The information from the front radars is combined with data from a windscreen-mounted camera to calculate the likelihood of an impact. The system uses escalating measures at certain critical points to try to help the driver avoid an accident. Firstly, when the system calculates that a collision is likely, it issues optical and acoustic warnings and pre-fills the braking system in preparation for an avoidance manoeuvre by the driver. If the driver does not react and the criticality increases a further warning is given: a small braking jolt serves as a ‘haptic’ warning, encouraging a driver reaction. At the same time, the brakes are prepared so that if the driver does brake, to whatever extent, the system will automatically apply the appropriate braking force to avoid or mitigate the collision. At the same time, slack is removed from the seat belts. If there is still no reaction from the driver, the system applies partial braking to try to mitigate a collision. Finally, when an accident can no longer be prevented, the system autonomously applies maximum braking to reduce the severity of the collision. The hazard warning lights are automatically turned on to warn other road users. The system is designed to operate at speeds up to 200 km/h.
Another known system, which helps to avoid or to mitigate accidents at speeds up to 30 kilometers per hour (kph) uses a lidar (Light Detection And Ranging) sensor positioned at the top of the windscreen. This scans the area up to around 7.6 m ahead of the vehicle for possible obstacles. If the vehicle detects a braking, slower-moving or stationary vehicle in front and it determines that a collision is likely, the brakes are pre-charged. If the driver remains inactive (no steering or braking input), the car applies the brakes automatically and reduces engine torque.
At relative speed differences less than 15 kph the system may help the driver to entirely avoid the collision with the obstacle in front. If the relative speed difference between the two vehicles is between 15 and 30 kph the impact is unavoidable through braking alone but the system will aim to reduce speed prior to the impact. If the driver intervenes to try to avoid the accident, either by accelerating hard or by steering, the system deactivates.
The foregoing description applies primarily to the situation where the vehicle is detecting an object such as another “object vehicle” which the vehicle (henceforth the “subject vehicle”, being the vehicle in which the emergency braking system is fitted) is following. Systems for detecting object vehicles are reasonably robust and it is unlikely (and this is very important) that there will be any false-positives in the sense of detecting something and applying the brakes, either temporarily or fully, when there is no object to be detected.
However, camera image processing technology is becoming sophisticated enough to reliably detect, with a high probability of being correct, adult pedestrians. Thus some braking systems are invoked when pedestrians are detected in the path of a subject vehicle. Again, such invocation cannot reasonably be commenced before a collision becomes inevitable because drivers need to remain in control of, and be responsible for the driving of, their vehicles. It is simply not acceptable for the vehicle unnecessarily to take control itself. On the other hand there are measures that can be taken. For example the braking system can ready itself for emergency braking by a preliminary pressurisation of the braking system, so that when the brake pedal is pressed, braking is instantaneous. Also, driver braking can be assisted by applying the brakes harder than the driver applies if the system calculates that faster braking is possible.
Thus, instead of detecting other vehicles, some known systems are designed to detect pedestrians and other vulnerable road users. Images from a forward-looking camera are analysed to identify shapes and characteristics typical of humans. The way in which they are moving relative to the path of the vehicle is calculated to determine whether or not they are in danger of being struck. If so, the IEB system applies full braking to bring the car to a halt and, at the same time, it may issue a warning to the driver. Predicting human behaviour is difficult and the algorithms used in pedestrian detection systems are very sophisticated. The system must be able to react properly to a valid threat but must not apply the brakes where there is no danger e.g. where a pedestrian is walking to the edge of the pavement but then stops to allow the car to pass. These systems invariably employ a camera combined with a radar “sensor fusion”. New technologies are appearing on the market that use infra-red and can also operate in very low light conditions.
Euro NCAP (www.euroncap.com) was established in 1997, and is composed of seven European Governments as well as motoring and consumer organisations in every European country. Euro NCAP organizes crash-tests and provides motoring consumers with a realistic and independent assessment of the safety performance of some of the most popular cars sold in Europe. Euro NCAP makes recommendations and sets standards that automatic braking systems need to meet to be approved by Euro NCAP before they can become marketable products for use in vehicles. Presently, pedestrian recognition systems must, with a substantial level of confidence (as much as 98% or more), be capable of identifying pedestrians greater than 1.2 meters tall. It is not a requirement that systems recognise smaller pedestrians such as children. This is obviously not because children are unimportant, but simply reflects the reality that technology is not precise enough to reliably distinguish small humans from other objects of a similar size.
The 98% level of confidence calculated by the system is the probability that a detected object is a pedestrian. Needless to say, if an object such as a small child is reliably identified as such, with that level of confidence, then brakes will be automatically applied in appropriate circumstances as discussed above (or as particular manufacturers prefer). However, it is not expected that reliable identification can be guaranteed for pedestrians (objects) less than 1.2 meters tall.
In 2014 calendar year all new cars that are launched into the market will be tested under new Euro NCAP rules. The effect of the new testing will be that a car must provide a level of autonomous collision avoidance and autonomous collision mitigation with another car if it is to be rated as a 5-Star vehicle.
However, camera systems that are capable of delivering such discrimination are fundamentally very complex and sophisticated and necessarily expensive. A far less sophisticated camera system is employed to recognise road signs and warn drivers of speed limits and the like. Recognising road signs is relatively trivial and can be achieved by a less sophisticated camera system.
Parking Distance Control (PDC) systems typically employ ultrasonic sensors. These are short range devices and are used to give warning of very close objects around a vehicle to assist a driver in parking or close manoeuvring of a vehicle. JP-A-2008/049932 appears to disclose the use of ultrasonic sensors and cameras to assist in manoeuvring of a vehicle including applying brakes when an object is about to be hit. PDC systems can prevent collisions when the vehicle is travelling as fast as 8 or 9 kph. The reason for this is that the range of current ultrasonic systems is little more than about 4 meters, so at speeds beyond about 15 kph the time permitted is generally insufficient even to mitigate the effects of a collision. However, coded ultrasonic sensors can increase the range of ultrasonic devices to up to 15 or 20 meters. Ultrasonic systems employ an ultrasonic transceiver that detects reflections of ultrasonic pulses. Such systems can be susceptible to many false positives. They require time in which to analyse signals received and to filter out spurious reflections from items which lie outside the path of the vehicle, e.g. street furniture etc.
It is an aim of the present invention to provide an improved IEB system.